182 DE. WILLS AND MK. SMITH ON THE LOWER [vol. Ixxviii, 



add Calymene lilanimarcjinaia (/) Reed, Ortliis {Platystropliia^ 

 hiforata Schlotheim, OrtJiis {I>almanella)Q,l. testudinaria Dsi\Yna.n, 

 Cryptograptiis of. scliciferi Lapworth, and Diplograptus {Glypto- 

 yrcq)tus) teretuisculus (Hisinger). 



The graptolites were found by Mr. W. B. E,. King in the lower 

 part of the series near Pandy, and in Miss EUes's opinion suggest 

 a Llandeihan age — possibly even the zone of T>iplo(jra2')tu8 iere- 

 tiusGuhis. On the other hand, the JPlectamhonifes sericea from 

 slightly higher beds is pronounced by Prof. 0. T. Jones to be 

 simila]' to the Soudlej^-Sandstone form of this species. 



Until further evidence of the exact age is forthcoming, the 

 Cwm-cluyd Ash at the bottom of the Teirw Beds, in that it occurs 

 on the south as well as on the north of the Berwyn Anticline, 

 forms the most convenient base to the Bala Series in this district. 



(8) The Pandy Ash. — The Pandy Ash, although variable in 

 thickness, forms a useful horizon for mapping. It contains frag- 

 ments of keratophyre in its coarser parts, and forms the highest 

 ash at the Falls of the Ceiriog, where it was formerly regarded as 

 the 'Little Ash' of Jukes (that is, perhaps, the Pen-j'-'graig Ash). 



(4 & 5) Brjm Beds and Pen-j^-graig Ash. — As pointed out 

 by Dr. Grrooin & Mr. Lake, the Brjai Beds vary considerabl}'" in 

 thickness and composition from east to west. From place to place, 

 the rocks are penetrated by sills of lime-bostonite, the best-known 

 example being the Coed-y-glyn Sill near G-lyn- Ceiriog. The base 

 of the Bryn Beds overlies the Pandy Ash. On the west of the 

 Grljai valle}'', at least as far west as Tomen-y-bwlch (1^ miles west- 

 south-west of Nantyr), and possibly farther, under the cover of 

 peat, theu' summit is at several places proved to be defined by the 

 ' Pen-y-graig Ash ' of Groom & Lake. This is a thin, usually 

 sheared, keratophyric ash, which is, perhaps, impersistent between 

 the known limits of its outcrops. Throughout the western region, 

 the Bryn Beds are rather uniformly dark-blue sandy mudstones or 

 sandstones, often yielding abundant fossils. 



East of the Grlyn Yalley the upper part of the group is, in the 

 main, similar in litholog}^, but is underlain by a series of shales 

 containing numerous bands of felspathic sandstone, which increases 

 the total thickness of the Bryn Beds very considerably (see 

 Table II, p. 189, & fig. 3, p. 185)"; The Pen-j^-graig Ash is,''in our 

 opinion, absent in this region. In adopting this view we differ from 

 Dr. Groom & Mr. Lake, for they regarded an ash which occurs 

 above a massive sandstone at Brj^n (in Nant-Iorwerth, south-east 

 of Glyn-Ceiriog) as the Pen-y-graig Ash. The ash at Bryn, 

 however, does not form the top of the Bryn Beds here, nor does it 

 closely resemble the Pen-3^-graig Ash. In our opinion, the 

 following sequence can be established for the Bryn Beds near Bryn 

 (see fig. 2, p. 184). It is of interest, as providing evidence of local 

 contemporaneous movements. 



